1. Field of the Invention
This invention relates to highly filled blends and more specifically, it relates to highly filled blends of ethylene interpolymers modified with processing oil.
2. Description of the Prior Art
The use of processing oils with natural rubber or synthetic rubber-like compounds containing sulfur, accelerators, carbon black and other additives customarily used in the rubber industry is well known. In some instances in order to obtain very high tensile strength values, fillers are omitted. On the other hand, it is known that styrene/butadiene rubber (SBR) compounds, such as are used to adhere jute secondary backings to carpets, can readily hold up to 80% by weight or more of calcium carbonate filler. Vulcanization or curing enhances blend strength.
For thermoplastic elastomeric uses it is desirable both to avoid curing and to employ fillers to reduce blend costs, as well as to increase blend density.
Binary blends of ethylene/vinyl acetate (EVA) copolymer with filler are known as articles of commerce. The practical limit for addition of a filler such as the more commonly employed medium density fillers, e.g. CaCO.sub.3, bauxite, gypsum, etc., is about 60% by weight, even when using a relatively low melt index (higher molecular weight) resin, or softer, higher vinyl acetate grades. As filler levels rise, other properties suffer, such as melt index (as it drops, extruder pressures mount rapidly), softness (the "hand" becomes much stiffer), and elongation (which drops alarmingly). Ultimately, at about the 70% filler level, it is not possible to compound binary EVA/Whiting (naturally occurring ground limestone, CaCO.sub.3, from Georgia Marble Company) blends as the mixture will no longer "flux" in a Banbury Mixer (the charge merely stirs--the resin will not "work" as the blades turn, no power rise ensues, the mixture on discharge is still discrete EVA pellets in a powdery Whiting mass). If one were to use a very dense filler, such as BaSO.sub.4, approximately 10% by weight more filler can be added to binary EVA blends.
Industrial noise and its control are items of increasing concern to governmental, environmental, and industrial organizations. Governmental agencies are establishing noise limits to which workers may be exposed to protect their health.
From an aesthetic standpoint, noise also presents problems. Advertisements for "quiet riding" automobiles are ubiquitous. Manufacturers are attempting to make other vehicles quiet as well--including campers, trailers, buses, trucks, and off-road-use farm vehicles.
It has long been known that interposing mass between a sound source and the area to be kept quiet is an effective means for attaining sound deadening. A stone wall is extremely effective--but is not often practical. A sheet of lead is thin, flexible, often highly effective, but costly. The challenge, then, is to attain a dense, thin, flexible sheet which can be interposed between a source of noise and the area to be quietened.
Sheets of thermoplastics or of rubberlike materials have long been used as sound-deadening means. To make the sheets flexible, dense, strong, and inexpensive has posed a challenge to compounders for many years. For some uses, such as automobile carpet underlayment, the sound-deadening sheet must also be moldable.
Schwartz U.S. Pat. No. 3,904,456 is related to a method for inhibiting transmission of airborne noise by interposing in the air space between the noise source and the location to be insulated a thin, dense normally self-supporting film or sheet composed essentially of from about 10 to about 40% by weight of ethylene/vinyl acetate copolymer having an average vinyl acetate content of from about 10 to about 42% by weight and a glass transition temperature of at least about 30.degree. C. below the average ambient temperature in the air space, and from about 60 to about 90% by weight of inorganic filler materials, such as sulfates, carbonates, oxides, etc. of barium, calcium, cadmium, etc., effective to produce an overall density greater than at least 2 grams per cubic centimeter.
EVA copolymers have been used industrially for nearly two decades, however, they are not known to be used in conjunction with processing oils as articles of commerce. This could well be an outgrowth of the way EVA commercialization has proceeded. That is, most EVA blends are based on EVA/paraffin wax technology, where paraffin wax weight is often up to ten times the weight of the EVA present. Furthermore, despite the obvious savings inherent in using lower-cost, lower-quality waxes, such as scale wax or slack wax, all attempts to do this have failed. The reason was always the same--the oil content of the wax migrated and destroyed the effectiveness of the coatings or adhesive when the oil reached the bond or sheet surface. Thus, compounders "knew" that oil could not be used in EVA blends and technology developed along other lines.
Rundle U.S. Pat. No. 3,497,375 discloses coating compositions for wooden concrete molds consisting of ethylene/vinyl acetate copolymer and paraffinic oil. There is no filler employed in the coating compositions of this patent.
Monaghan U.S. Pat. No. 3,379,193 discloses teeth covers made of ethylene-vinyl acetate copolymer in itself or in combination with mineral oil and, if desired, with fibers and coloring materials. The preferred formulation is disclosed to be 47% by weight of ethylene-vinyl acetate copolymer, 47% by weight of mineral oil, 5% by weight of nylon fibers, and 1% by weight of titanium dioxide.
German Patent Application No. 2,319,431 discloses sound deadening composites suitable for use in automobiles which consist of a highly filled polymer sheet (for example, 300-1200 or even up to 1500 parts of filler per 100 parts of polymer) which on its backside is provided with a filler material sheet, e.g., a polymer foam. Suitable polymers for use are disclosed to be terpolymers of ethylene, propylene and non-conjugated diene (EPDM), polyvinyl chloride (PVC), mixed polymers of ethylene and vinyl acetate (EVA), styrene-butadiene mixed polymers (SBR) and mixtures of these materials with thermoplastic polymers, such as polystyrene and polyolefins.
Boyer U.S. Pat. No. 3,010,899 discloses blends of ethylene/vinyl acetate resin and mineral oil which are either rubbery or grease like depending upon the proportion of oil to resin and can be used as a substitute for crepe rubber or as a grease. It is further disclosed that fillers such as carbon black or finely divided clays can be added to the rubbery products to increase hardness and produce materials suitable as floor tile. As indicated for example in Claim 11, the filler, carbon black, is present in a "minor amount" while the oil-ethylene/vinyl acetate copolymer mixture is present in a "major amount". In Example 2 an oil+resin/carbon black ratio of 4 parts by weight to 1 part by weight is indicated.
Rosenfelder U.S. Pat. No. 3,203,921 discloses the use of compositions consisting essentially of 73-88% by weight of a homo- or copolymer of ethylene (which can be ethylene/vinyl acetate or ethylene/ethyl acrylate copolymer), 2-7% by weight of an aliphatic paraffinic hydrocarbon mineral oil and 10-20% by weight of a mineral filler, (for example, calcium carbonate, barium sulfate, etc.) for preparing blow-molded objects such as dolls.